Bitcoin is pseudonymous. Monero is on a whole different level. Reducing the anonymity set requires you to forcibly (rubberhose cryptanalysis or some sort of extremely exotic brute force attack) reveal one or both of the user's public keys, and THEN to use some sort of exotic attack to weed out and isolate the true signatures in the ring groups of every output the user has ever created. It is practically improbable, barring some extremely powerful and extremely exotic attack on the cryptographic primitives used in Monero.